Growth of the postal system was forced to follow the growth of the country itself to assure the ability of all Americans to send and receive mail. By the time of the Civil War, most private postal services were closed. The California Gold Rush brought the need for transcontinental mails: Steamships provided service by way of Panama; overland coach reduced mail transit to 20 days; the private Pony Express offered service as short as six days; and the railroad in 1869 provided seven-day service between New York and San Francisco.
Mail was retrieved and delivered by whatever means would work for an area, utilizing existing forms of transport wherever possible. Thus, paddle wheel steamers that called at river towns became part of the system. Air mail first was tried in 1911. By 1924 the New York-San Francisco route was flown regularly. After World War II, rapid expansion of air mail service and the reduction of the railway mail service changed the approach to mail transportation in the nation.
Development of the automobile changed the ability to delivery mail to people not residing in cities and towns. Rural Free Delivery (RFD) became permanent in 1896 on a nationwide basis. By 1915 the number of automobiles in RFD service allowed extensions of rural route. By 1920 RFD routes numbered 43,445. Because of farmers' demands, a national parcel post service began in 1913, which stimulated the mail-order business.